The present invention relates generally to delayed turn-off switching circuitry, and more particularly, toward thyristor controlled circuits for de-energizing a lamp or other load in a predetermined period of time following operation of a manual, automatic or electronic turn-off switch.
A need typically arises for a delayed turn-off circuit for a lamp or other load wherein the lamp is de-energized in a predetermined period of time following operation of a switch. For example, it is sometimes necessary to move between rooms in a house in the dark. It is desirable to have a lamp in one of the rooms remain on for a predetermined period of time after turn-off of the lamp, so that individuals may have adequate time to arrive at the second room in the light.
Prior art delayed turn-off switches of which I am aware involve electro-mechanical components such as dashpots, which wear-out after extended use, and over relatively short periods of time. Electronic systems to effect delayed turn-off of which I am aware utilize relatively involved unijunction transistor circuits that are used to control thyristors or power transistors. These circuits require the use of a large number of electronic components, decreasing overall reliability.
Accordingly, a primary object of the invention is to provide a new and improved delayed turn-off switching circuit for lamps and other electric loads.
Another object is to provide a new and improved delayed turn-off switch that is simple and reliable, and does not involve complex unijunction transistor circuitry.
Another object is to provide a new and improved delayed turn-off switching circuit which is highly reliable and uses no mechanical parts, such as dashpots.